<!-- Licensed under a BSD license. See license.html for license -->
<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=yes">
    <title>Three.js - Canvas Textured Cube</title>
    <style>
    html, body {
        height: 100%;
        margin: 0;
    }
    #c {
        width: 100%;
        height: 100%;
        display: block;
    }
    </style>
  </head>
  <body>
    <canvas id="c"></canvas>
  </body>
<!-- Import maps polyfill -->
<!-- Remove this when import maps will be widely supported -->
<script async src="https://unpkg.com/es-module-shims@1.3.6/dist/es-module-shims.js"></script>

<script type="importmap">
{
  "imports": {
    "three": "../../build/three.module.js"
  }
}
</script>

<script type="module">
import * as THREE from 'three';

function main() {
  const canvas = document.querySelector('#c');
  const renderer = new THREE.WebGLRenderer({canvas});

  const fov = 75;
  const aspect = 2;  // the canvas default
  const near = 0.1;
  const far = 5;
  const camera = new THREE.PerspectiveCamera(fov, aspect, near, far);
  camera.position.z = 2;

  const scene = new THREE.Scene();

  const boxWidth = 1;
  const boxHeight = 1;
  const boxDepth = 1;
  const geometry = new THREE.BoxGeometry(boxWidth, boxHeight, boxDepth);

  const cubes = [];  // just an array we can use to rotate the cubes
  const ctx = document.createElement('canvas').getContext('2d');
  ctx.canvas.width = 256;
  ctx.canvas.height = 256;
  ctx.fillStyle = '#FFF';
  ctx.fillRect(0, 0, ctx.canvas.width, ctx.canvas.height);
  const texture = new THREE.CanvasTexture(ctx.canvas);

  const material = new THREE.MeshBasicMaterial({
    map: texture,
  });
  const cube = new THREE.Mesh(geometry, material);
  scene.add(cube);
  cubes.push(cube);  // add to our list of cubes to rotate

  function resizeRendererToDisplaySize(renderer) {
    const canvas = renderer.domElement;
    const width = canvas.clientWidth;
    const height = canvas.clientHeight;
    const needResize = canvas.width !== width || canvas.height !== height;
    if (needResize) {
      renderer.setSize(width, height, false);
    }
    return needResize;
  }

  function rand(min, max) {
  if (max === undefined) {
    max = min;
    min = 0;
  }
    return Math.random() * (max - min) + min;
  }

  function randVelocity() {
    return rand(2, 4) * (rand(2) < 1 ? -1 : 1);
  }

  const maxLines = 60;
  const points = [
    { position: [rand(256), rand(256)], direction: [randVelocity(), randVelocity()]},
    { position: [rand(256), rand(256)], direction: [randVelocity(), randVelocity()]},
  ];
  const lineHistory = [];
  let lineCursor = 0;

  function drawCurrentLine() {
    const line = lineHistory[lineCursor];
    ctx.beginPath();
    ctx.moveTo(...line[0]);
    ctx.lineTo(...line[1]);
    ctx.stroke();
  }

  function drawLines(time) {
    points.forEach((point) => {
      point.position.forEach((position, ndx) => {
        const newPosition = position + point.direction[ndx];
        if (newPosition > 255) {
          point.direction[ndx] = rand(-2, -4);
        } else if (newPosition < 0) {
          point.direction[ndx] = rand( 2,  4);
        }
        point.position[ndx] = newPosition;
      });
    });
    if (lineHistory.length === maxLines) {
      ctx.lineWidth = 3;
      ctx.strokeStyle = '#FFF';
      drawCurrentLine();
    }
    lineHistory[lineCursor] = points.map(point => point.position.slice());
    ctx.lineWidth = 1;
    ctx.strokeStyle = hsl(time, 1, .5);
    drawCurrentLine();
    lineCursor = (lineCursor + 1) % maxLines;
  }

  function hsl(h, s, l) {
    return `hsl(${h * 360 | 0},${s * 100 | 0}%,${l * 100 | 0}%)`;
  }

  function render(time) {
    time *= 0.001;

    if (resizeRendererToDisplaySize(renderer)) {
      const canvas = renderer.domElement;
      camera.aspect = canvas.clientWidth / canvas.clientHeight;
      camera.updateProjectionMatrix();
    }

    drawLines(time * 0.1);
    texture.needsUpdate = true;

    cubes.forEach((cube, ndx) => {
      const speed = .2 + ndx * .1;
      const rot = time * speed;
      cube.rotation.x = rot;
      cube.rotation.y = rot;
    });

    renderer.render(scene, camera);

    requestAnimationFrame(render);
  }

  requestAnimationFrame(render);
}

main();
</script>
</html>

